The invention relates to a piezo-electrically driven clock oscillator.
In recent years, great reductions in cost, size and weight have been achieved in various information equipment including portable computers, personal digital assistants (PDAs), and mobile communication systems such as mobile telephones. As a result, the size and thickness of piezoelectric and voltage-controlled oscillators for use in these devices must be reduced. U.S. Pat. No. 5,745,012 to Oka, et al. shows a conventional piezoelectric oscillator employing a quartz-crystal resonator as a piezoelectric resonator and a conventional voltage-con-trolled (crystal) oscillator (VCXO). In the conventional quartz-crystal oscillator, a CMOS IC chip is mounted by a conductive adhesive on an island that is a part of a lead frame. The IC chip is electrically connected to input/output lead terminals by wires. A quartz-crystal resonator includes a cylinder shaped quartz chip and is electrically connected to the gate electrode and the drain electrode of the IC chip. The IC chip, the quartz-crystal resonator and parts of input/output lead terminals are molded by transfer molding with an epoxy resin molding resin to form a plastic package of the quartz-crystal oscillator. In another conventional voltage-controlled oscillator, electric circuit components such as a transistor and variable-capacitance diode are mounted on a substrate that is fixed by solder on the stem of a metal can package. A quartz-crystal resonator is also mounted on the substrate. The can is hermetically sealed by resistance welding for example. In another common type, a trimmer capacitor or the like is provided on the substrate and an adjusting hole is formed in the can so that the frequency may be adjusted after the voltage-controlled oscillator is mounted on a circuit board installed in a device such as a mobile communication system.
In the conventional piezoelectric and voltage-controlled oscillators described above, the piezoelectric resonator is accommodated in a cylinder case having a diameter of about 3 mm. As a result, the piezoelectric or voltage-controlled oscillator has a large height such as about 4.5 mm to 7 mm. Thus, its total volume is as great as 0.5 cc to 1.0 cc. The conventional piezoelectric and voltage-controlled oscillators of this type does not meet the small-size requirements that are essential in small-sized electronic devices such as PDAs, portable computers or mobile wireless devices such as cellular telephones. Also, crystals are expensive and there is difficulty in designing and producing a low cost piezoelectric element (such as a quartz chip) having such a small size while maintaining the required performance.